WASHINGTON (AP) -- Elderly Americans should be careful about giving out their Social Security numbers, officials warned Tuesday after arresting a man who sent out letters offering an extra check to senior citizens who send back money or their bank account and Social Security numbers.

"People should be really cautious about who they give their personal information to, especially their Social Security number," said Social Security Administration spokeswoman Cathy Noe.

Special agents from the Social Security inspector general's office arrested Anthony David Williams, 32, in Phoenix Monday night. Williams is accused of misrepresenting himself as a government employee to defraud retirees and disabled Americans receiving Social Security benefits. He is charged with mail fraud.

Calls to Phoenix phone numbers associated with Williams' businesses and to his lawyer on Tuesday were not immediately returned.

Williams allegedly mailed out letters on a likeness of Social Security stationery, often following up with phone calls, according to an affidavit filed in U.S. District Court in Phoenix.

"According to our records you are entitled to receive an additional check from Social Security each month," one version of the letter said. "These extra income benefits could give you up to an additional $514 per month."

Recipients were asked to send a "filing fee" of varying amounts up to $23, or to fill out a form including their Social Security and bank account numbers so the fee could be "automatically deducted."

The mailings were signed by "Donald Jenkins" of the "Winning Advantage Program, SSI-SSA" -- an alias used by Williams, who is British but applied last year to become a permanent U.S. legal resident.

Social Security recipients usually do get letters from the government when their benefits go up. Other legitimate mailings that people get from Social Security include a new statement of taxes paid and future benefits due, which every American worker over age 25 will receive by the end of next year.

"But we never ask for money for a processing fee," said Noe.

The federal government also does not normally ask for someone's Social Security number -- they already know it. Indeed, Social Security prints that number as an identifier on mailings about a person's benefits.

Social Security numbers are the most widely used ID in the private sector as well -- requested on the forms people fill out for everything from college registrations to bank slips. But consumers should remember that businesses can't require a person to disclose the number, Noe said -- although you may be refused a loan or credit card if you won't.

Social Security officials said they're not sure how many senior citizens Williams contacted. But federal agents reported seeing him, driving a silver, 1998 Lincoln Town Car, pick up responses from Oklahoma, Florida and Texas at a commercial post-office box. The agency also has received complaints from Michigan, Nevada and Indiana.

Lana Elzy of Floyds Knobs, Ind., contacted her local Social Security office after her 90-year-old aunt received an overnight mail package asking for her Social Security number, information about her bank account and her signature on a blank form.

Elzy, an accountant, recognized the blank form as a check template.

"If she had sent this back, the gist of it was he had all the information to get on the phone and call her bank, find out how much money she had, print the check and it was already signed," Elzy said.

The Better Business Bureau in Phoenix has received complaints about other mailings and telemarketing projects Williams is believed associated with, including from the "Rainbow International Lottery Service" and "Magic Numbers."

The company reportedly contacts people by phone offering membership in a lottery club or telling them they have won a lottery and must pay taxes to receive the money, the bureau said.